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Registered Member #105
Joined: Thu Feb 09 2006, 08:54PM
Location:
Posts: 408
I was looking at the 811A datasheet for a new tesla coil, and people say that they run them off from a MOT- however, the voltage on the datasheet is only 1500V max. Are people just running them with the output of the mot rectified and not level shifted to leave the output at around 2000V even though this is still above the tube rating?
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
Most people run them directly off the mot (2kv), although I have found that they will take the 4..5kv from a voltage doubled mot :) Really the only thing you need to watch out for is tank capacitance, which sets how many tubes in parallel you need. With .5nf you can run with a single tube off a mot, but if you want to run with a voltage doubled one you are going to need 2 in parallel. Good Luck!
Registered Member #212
Joined: Sun Feb 19 2006, 05:42PM
Location: Texas
Posts: 20
I personally saw an old VTTC built in the 1960s by a fellow radio collector using two 811As and a huge 4000V transformer. Either it worked off 4kV somehow or he used the center tap for 2kV instead. It worked well, gave out about 6-7" sparks.
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
In that case I would recommend a pair of 811a'a running off a full wave rectified mot and a .3nf tank cap or so to get sparks in the 4" range. Running CW is going to be a pain, because you are going to have much higher average powers than the coils running strait off a mot...
BTW, I am using a secondary that is 2.7" by 5" would with 32awg wire and it heats up to about 140F when running with .5nf on an unrectified mot, so I would recommend using relatively large wire. The pvc form actually expands almost 1/8" during runs
Registered Member #105
Joined: Thu Feb 09 2006, 08:54PM
Location:
Posts: 408
Im trying to get some 28 wire, so that should be good i think. Why go to two? I really wanna be simple and stick with one- also keep costs down. I can just adjust stuff to get small sparks rather than going with two tubes, right?
Registered Member #99
Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637
EDY19 wrote ...
Im trying to get some 28 wire, so that should be good i think. Why go to two? I really wanna be simple and stick with one- also keep costs down. I can just adjust stuff to get small sparks rather than going with two tubes, right?
Yup, im doing the same thing right now. Ive gotten about 2.5inchers with very crude tuning and no tweaking with one 811a....
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
As a baseline, be sure to check Steve Ward's dual 811A coil. (Search google for his website) I believe his circuit is based on John Freau's original schematic.
Registered Member #105
Joined: Thu Feb 09 2006, 08:54PM
Location:
Posts: 408
Ok, Ill check that- I also read through the FAQ on steve wards site- very informative for someone who isn't much into tubes!!! The schematic I am looking at is this one- and I have identified which component is which when compared with steves basic circuit so I can get proper ratings etc. Does this one look alright? Also I'm thinking grid leak anywhere inbetween 30k and 50k ohm range? Heres the schematic:
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811A tube coil
